Where's winter?

We've been finding winter pretty mild so far this year (well, this morning was a touch brisk at 1C, but overall, mild!). One of the reasons for that is that we now have insulation in the roof, meaning the house is a bit easier to heat. The other reason is that minimum temperatures just haven't got that cold yet. I had a look at NIWAs database to see if it really is warmer than previous years. As a rough guide, I picked the date of the first frost. I've taken this to be an air temperature below zero, even though frost might form on the ground with an air temp just above zero (the ground can be a couple of degrees colder, at least partly depending on moisture levels). So, the dates of the first frosts for the last 10 years, in Hamilton city (not out at the airport - it's colder out there!):

• 2001: 17/5
• 2002: 17/7
• 2003: 14/5
• 2004: 8/4
• 2005: 22/4
• 2006: 17/5
• 2007: 29/5
• 2008: 7/5
• 2009: 10/4
• 2010: 18/3
• 2011: ? Haven't had one yet!

So, 2002 was a very late one, but otherwise, it's typically around the middle of May. And this year is mild. At least so far. We do definitely get frost every year, so it's going to come sometime... even if it is in July!

PS: maximum temperatures have been reasonably typical for winter (around 15 most days, sometimes colder)